Drip irrigation hose or tape has been available now for several years. Typically, agricultural drip tapes are formed from relatively thin, flexible, continuous plastic strips folded over and seamed along a longitudinal edge to establish a primary flow path. One or more secondary flow paths are typically formed within the primary flow path by fixing discrete emitter devices along the length of the tape or hose, or by applying parallel strips of plastic material within the hose interior (for example, in the area of the longitudinal edge overlap) to form a secondary flow path. It is generally the case that the primary flow path is connected to the water supply with inlets and outlets to and from the secondary flow path, so that water flows from the primary path to the secondary flow path, and then out of the drip tape in a controlled fashion. Some tape or hose constructions incorporate turbulence inducing regions in the secondary flow path to prevent clogging and reduce the sensitivity of the flow rate to pressure changes.
Drip irrigation hoses or tapes are well represented in the patent literature, and examples may be found in U.S. Pat. Nos. 3,870,236; 3,896,999; 4,009,832; 4,247,051; 4,430,020; 4,473,191; 4,874,132; 4,880,167; 4,984,739; 5,163,622; 5,181,532; 5,203,503; 5,207,386; 5,282,578; and 5,333,793.
Despite the wealth of innovative drip irrigation technology, significant areas of concern remain relating to reliability and cost. For drip tape to be effective and commercially viable, it is essential that the secondary flow path not become clogged with solid matter in the water supply, or by outside debris blocking the outlets. At the same time, to be commercially viable, drip tape must be economical to manufacture.
In commonly owned, co-pending application Ser. No. 08/570,014, filed Dec. 14, 1995, there is disclosed a new and improved drip tape construction which offers advantages not found in the drip tape constructions of which we are presently aware. In the exemplary embodiment, the tape is formed by a strip of flexible PE material folded over and seamed along overlapped longitudinal edges. Interiorly of the tape, and in an area remote from the overlapped seam, there is a pre-formed longitudinally extending plastic bead or strip which defines a series of axially spaced secondary flow paths.
Each secondary flow path has a secondary flow channel including inlet, turbulence inducing, and outlet regions, all of which are preformed on one side of the hot melt bead or strip. The pattern side of the bead is applied face down on the sheet so that the sheet wall itself closes the secondary flow channel except for a plurality of inlets formed in the bead at longitudinally spaced locations along the inlet region. These inlets are arranged perpendicular to the longitudinal axis of the tape, and thus also perpendicular to the secondary flow channel. The inlets are located on both sides of the secondary flow channel, in longitudinally spaced relationship, with the inlets on one side of the secondary flow channel offset longitudinally with respect to the inlets on the opposite side of the secondary flow channel. In this exemplary embodiment, the inlet region extends well over half the total length of the secondary flow path, but this dimensional relationship may vary.
The inlet region leads to a turbulence inducing region formed by a series of peaks and valleys on opposite sides of the secondary flow channel, in longitudinally offset relationship so that the peaks on one side of the secondary flow channel in this region project towards the valleys on the opposite side of the flow channel. The peaks projecting from both sides of the secondary flow channel lie along a line through the center of the secondary flow channel in the exemplary embodiment, thus creating a tortuous path which induces turbulence in the secondary flow path. It is this turbulence that dissipates energy and creates zero or near zero pressure discharge to atmosphere. The turbulence also prevents clogging of the secondary flow path by debris or other solid impurities within the primary water supply.
Downstream of the turbulence inducing region, an outlet region is provided which communicates with an elongated slit in the tape wall which allows the water in the secondary flow path to escape in a controlled drip-like fashion. The outlet region, or reservoir, is otherwise axially closed in the downstream direction, thus isolating the path from the inlet region of the next adjacent downstream secondary flow path, and thus also forcing all water to exit via the elongated slit in the tape wall. In the preferred arrangement, the secondary flow paths are formed of substantially transparent material, for reasons stated in the '014 application.